Conventionally, foam made of thermoplastic resin is used as an insulation material, a buffer material, and a floating material, since the foam is excellent in lightweight property, insulation property and flexibility. Among those, polyolefin-based resin foam, in particular, is widely used for such upholstery materials as doors, ceilings, instrument panels etc. of vehicles by secondary thermoforming, as the polyolefin-based resin foam is excellent in heat-resisting property, dimensional stability, and so on.
Further, in the Japanese Patent Laid Open No. 8-11254, composite foam suitable for upholstery materials for vehicles is suggested in which thermoplastic resin foam containing polyolefin-based resin foam is used.
However, in the above-mentioned composite foam, when an expansion ratio of the thermoplastic resin foam is raised in order to improve the lightweight property, bending strength and compression rigidity of the composite foam is lowered. Consequently, when the composite foam was used as a ceiling material of a vehicle, there was a problem that the composite foam was bended, flexed or broken at the time of manufacturing or installation in a vehicle, which resulted in a dent at a part to be fixed to the vehicle which further resulted in unstable installation.
Further, accessories of the vehicle such as a lamp were conventionally mounted to an upholstery material after the upholstery material was installed in the vehicle. However, a module system in assembling vehicles has advanced these years, in which the accessories such as the lamp are mounted to the upholstery material of the vehicle in advance, and the upholstery material provided with the accessories is installed in the vehicle. Accordingly, better bending strength and better compression rigidity are required than before for a use for the upholstery material.
In view of the above-mentioned problems, a purpose of the present invention is to provide a multi-layer sheet, which is excellent in bending strength, compressive strength, a thermoforming property and dimensional stability as well as a lightweight property, and to provide a manufacturing method of the multi-layer sheet and a molding method thereof.